I've made a coupe AR's out of Polymer lowers from Tennessee arms. Functionally I've never had a issue. The fit never seems to be as good as other lowers. The take down pins are usually much harder to get out and the upper fits tight initially. If your aiming for something light and cheap I wouldn't shy away but if your looking for a nicer finish they wouldn't be my first choice. Mine are both trunk monkeys that I don't have to worry about getting a little dirty.